The present invention relates generally to computer systems and more particularly to a system including hardware and firmware for controlling the switching of a digital computer system from a native mode of operation to a non-native mode of operation.
Generally, each process or program which an electronic data processor is to execute, is described in an entirely different series of steps. This series of steps is dictated by a plurality of variables, two of which are the hardware available within the data processor and the character configuration employed. The execution of a process or program written to maximize the capability of a given data processor in which the process is to run to minimize total machine time required to run such process is defined as the natural mode or native mode of operation of the associated electronic data processor. Therefore any program written for a particular processor can be written in a native mode of operation of that processor. Each time that a new data processing system is introduced, the problem is always raised as to whether the new data processing system will operate with the programs written for the native mode of operation of the old data processing system. Quite naturally, a new data processing system includes new hardware units and new concepts of data flow which are not found in the previous data processing system. Therefore, the programs written for the replaced systems are not operable in the native mode of operation of the new system.
Accordingly, any data processing system operating in response to both a first stored program, directing the operation of such system in the native mode of operation, and operating in response to a second stored program, directing the operation of the system in a substituted or non-native mode of operation wherein such first and second programs constitute a process, it is necessary to employ an efficient switching means for executing the desired one of the programs in the system. Such operation or program mode switching techniques are shown in U.S. Pat. Nos. 3,374,466 and 3,440,612.
It is accordingly an object of the present invention to provide an improved operating mode switching system for a data processing system by which native mode instructions and non-native mode instructions may be executed in the same processor.
It is a further object of the present invention to provide a multiprocessing computer system to efficiently switch between the execution of a native mode instruction and one or more non-native mode instructions.